DESCRIPTION: (verbatim from applicant's abstract) The goal of this project is to develop a range of techniques to study drug transport across biological barriers. A continuum of techniques from in vitro model systems through in vivo animal systems will be developed. The techniques will be based on a combination of microdialysis sampling and capillary electrophoresis. These techniques will provide methods for high throughput screening in early drug development that will be correlated to in vivo studies. A high throughput method based on vesicular and cell-modified capillary electrophoresis (CE) will be developed. In this technique, vesicles, either artificial or biologically derived, or cells will be used as migration modifiers in CE. Partitioning of the test compounds into the vesicles or cells will modify the migration of the test compounds based on their permeability into the vesicle or cell. The change in migration relative to normal CE should correlate to membrane permeability. This approach will provide high throughput by allowing simultaneous permeability determinations of compounds in a mixture. We will also develop in vivo microdialysis techniques using cell culture models of biological barriers. The diffusion cell approach to using cell culture models to determine permeability will be modified by growing the cells on microdialysis probes. This will improve the throughput of cell culture techniques by improving the mass transport in the system. In addition, the continuous sampling capabilities of microdialysis will provide for kinetic determinations as well as equilibrium measurements. Cell-coated microdialysis probes will also be reusable. Finally, work will continue on the in vivo studies using microdialysis sampling to study transport across biological barriers in vivo. The focus will be on transport across the gastro-intestinal mucosa, across the placenta, and across the blood-brain-barrier. The same set of test compounds will be used in all of the in vitro and in vivo studies to provide an in vitro to in vivo correlation. The development of these methods will also provide a continuum of techniques of increasing complexity but decreasing throughput.